Device and method for hydrogen storage

Abstract

A device (1) for hydrogen storage, comprising: a semiconductor substrate (2); at least one pillar (10) arranged on the semiconductor substrate (2), the at least one pillar (10) comprising a core (12) and a shell (14), the core (12) of the pillar (10) comprising a semiconductor material, and the shell (14) of the pillar (10) surrounding the core (12) of the pillar (10), the shell (14) comprising Mg3N2, and / or a plurality of GaN particles (16).

Description

Technical Field

[0001] The present inventive concept generally relates to devices and methods for hydrogen storage. Background Art

[0002] Hydrogen is considered a clean and sustainable energy source, and storing hydrogen under ambient conditions is a focus area of research and development. For example, a challenge for the widespread commercialization of fuel cell electric vehicles (FCEVs) and other hydrogen fuel cell applications is how to store hydrogen in a compact, reliable, and cost-effective manner.

[0003] One alternative for storing hydrogen includes large-volume systems for storing hydrogen in gaseous form. Storing gaseous hydrogen requires high-pressure tanks. Compressed hydrogen can be held, for example, at tank pressures of about 350 bar to 700 bar. Disadvantages of storing compressed gaseous hydrogen include a high energy penalty for compression, which may consume some of the total internal energy of the hydrogen. In addition, expensive carbon fiber for wrapping cylinders may be required to withstand pressures in the higher range. Other options for hydrogen storage can include liquefied hydrogen. Hydrogen has a boiling point of -252.9 °C, and to liquefy hydrogen, the temperature needs to be reduced to cryogenic temperatures. The liquefaction process may consume several tenths of the total internal energy of the hydrogen. When storing hydrogen in liquid form, it may also be difficult to prevent hydrogen loss through evaporation. Therefore, potential energy losses must be considered when using liquid hydrogen as an energy source.

[0004] Compared to other fuels, hydrogen has a higher energy density per unit mass. However, its low density at ambient temperature means lower energy per unit volume. Therefore, in order to be able to use hydrogen as an energy source on a larger scale, it is important to develop storage methods with the potential for higher energy density. Summary of the Invention

[0005] An object of the present invention is to provide hydrogen storage under ambient thermodynamic conditions. In addition, an object of the present invention is to facilitate the transportation of hydrogen, such as facilitating the low-cost transportation of hydrogen gas and / or facilitating the non-explosive transportation of hydrogen gas.

[0006] These and other objects of the present inventive concept are at least partially met by the invention as defined in the independent claims. Preferred embodiments are set forth in the dependent claims.

[0007] According to a first aspect, there is provided a device for hydrogen storage, comprising:

[0008] a semiconductor substrate,

[0009] at least one column arranged on the semiconductor substrate, the at least one column comprising a core and a shell, the core of the column containing a semiconductor material, and the shell of the column surrounding the core of the column, the shell containing:

[0010] Mg3N2 and / or

[0011] a plurality of GaN particles.

[0012] The inventors have recognized that hydrogen can be stored in solid materials. Metals or chemical hydrides exhibit high storage capacities but do not meet the requirements for fast kinetics and reversibility. Metal-organic frameworks (MOFs) can be used as storage materials due to their porosity, fast kinetics, and reversibility, but high pressure and low temperature are necessary for the adsorption process due to the weak adsorption energy of hydrogen molecules (mainly through van der Waals interactions), as described in RSC Adv., 2017, 7, 33953.

[0013] The inventors have recognized that hydrogen can be stored in Mg3N2 or GaN particles. Thus, such materials can be considered hydrogen storage materials. The inventors have further recognized that the hydrogen storage material in the form of a shell surrounding a core of a column can be particularly effective. Such an arrangement can enable hydrogen to diffuse into the shell and be stored in the shell or at the interface between the core and the shell. As described below, there can be several reasons why the device provides effective hydrogen storage.

[0014] When arranged as a shell surrounding a core of a column, the hydrogen storage material can have a large surface area to volume ratio. A large surface area to volume ratio can enable a large storage capacity. In the outermost part of the hydrogen storage material, i.e., near the outer surface of the hydrogen storage material, hydrogen storage can be the most effective.

[0015] A large surface area to volume ratio can, for example, facilitate the effective diffusion of hydrogen into the hydrogen storage material. The diffusion time can increase with the distance into the hydrogen storage material, for example, exponentially. Thus, when the hydrogen storage material is arranged as a shell surrounding a core of a column, the amount of hydrogen that can be stored can be high and / or the time taken to load the hydrogen storage material with hydrogen can be short.

[0016] In addition, the device facilitates the electrical control of hydrogen storage. For example, an electric field can be applied across the shell of the column by applying an electric potential to the core of the column. Such electrical control can enable reversible hydrogen storage. The electric field can be utilized to facilitate the binding and release of hydrogen. An electric field can be applied, for example, such that the binding of hydrogen is promoted. Then, the electric field can be reversed such that the release of hydrogen is promoted.

[0017] In view of the above, the device facilitates the transport of hydrogen. Hydrogen can be loaded into the shell in a loading step. Then the device can be transported together with the loaded hydrogen in a transport step. The transport can be safe because the risk of explosion when hydrogen is loaded into the shell can be low. Then, hydrogen can be released from the device in a release step.

[0018] The loading step can include:

[0019] Place the device according to the first aspect in a hydrogen atmosphere; and

[0020] Apply a first electric field across the shell of the column by applying an electric potential to the core of the column.

[0021] Then hydrogen can be adsorbed and / or absorbed by the shell. The adsorption or absorption can be assisted or caused by the first electric field herein.

[0022] The hydrogen absorbed by the shell can be retained in the volume of the shell by the shell, for example, uniformly distributed in the shell.

[0023] The hydrogen adsorbed by the shell can be retained on the surface of the shell. The surface of the shell can be the internal surface of the shell, for example, the surface between two layers of the shell, such as the surface between two crystalline layers of the shell. Alternatively, the surface of the shell can be the inner surface of the shell, for example, the interfacial surface between the shell of the column and the core. Alternatively, the surface of the shell can be the outer surface of the shell.

[0024] In the case where hydrogen is adsorbed by the shell, hydrogen can be attracted to the adsorption surface (e.g., the internal surface of the shell and / or the inner surface of the shell and / or the outer surface of the shell) by London dispersion forces. The London dispersion forces can be formed by a sheet of electrons formed at the surface of the material. An electron gas can be formed at the interface between the core of the column and the shell of the column. The electron gas can be a two-dimensional electron gas. The inventors have recognized that the two-dimensional electron gas can provide a potential energy well capable of binding hydrogen. According to the inventive concept, a semiconductor substrate having at least one column facilitates the formation of the potential energy well. The increased surface and the formation of the potential energy well allow an increased storage capacity. According to the inventive concept, the increased storage capacity allows for a greater volumetric efficiency and a greater mass storage efficiency. What can be achieved with the greater volumetric efficiency and the greater mass storage efficiency is that the inventive concept can be effectively implemented in transportation applications.

[0025] After the loading step, the device can be transported in a transportation step. The device can be transported, for example, without applying an electric field across the shell of the column. Hydrogen can still be retained by the shell without leakage or only slow leakage. Alternatively, the device can be transported with an electric field applied across the shell of the column.

[0026] After transportation, hydrogen gas can be released from the device in a release step. The release step can include:

[0027] Apply a second electric field across the shell of the column by applying an electric potential to the core of the column.

[0028] The second electric field can have a direction opposite to that of the first electric field. Then hydrogen can be released by the shell. The release herein can be assisted or caused by the second electric field.

[0029] The semiconductor substrate can comprise any semiconductor material, such as silicon, sapphire, silicon carbide or GaN. The semiconductor substrate can be a semiconductor substrate suitable for epitaxial growth. It can be particularly useful in the case of a silicon substrate. Silicon substrates are inexpensive and there are mature processing methods for silicon in the semiconductor industry. The semiconductor substrate can be a silicon <111> substrate or a silicon <100> substrate. Such substrates can be particularly suitable for epitaxial growth. In this context, <111> and <100> refer to the Miller indices of the substrate surface. The semiconductor substrate can have a different material from the semiconductor material of the core of the pillar. For example, the semiconductor substrate material can be silicon, sapphire or silicon carbide, and the material of the core of the pillar can be GaN or AlGaN. Any combination of the above semiconductor substrate materials and core materials is possible. Alternatively, the semiconductor substrate material and the material of the core of the pillar can be the same material, such as Si. Or, the semiconductor substrate material and the material of the core of the pillar can be any other combination of semiconductor materials.

[0030] In the following, the pillars of the device will be discussed. The pillars can be arranged vertically on the substrate. For example, the axis of the pillar can extend in the vertical direction. In this context, the vertical direction refers to the direction perpendicular to the substrate surface. Similarly, the lateral direction refers to the direction parallel to the substrate surface. The device can include more than one pillar. For example, the device can include a plurality of pillars. The plurality of pillars can be arranged vertically on the substrate. The plurality of pillars can be an array of pillars. The number of pillars per square mm can be at least 250,000.

[0031] In principle, the pillars can have any thickness. However, the diameter of the pillars can advantageously be less than 1 micron, preferably less than 100 nm. The diameter of the pillars in this context includes the shell. Thus, the pillars can be thin. As previously mentioned, the surface area of the hydrogen storage material can be increased by increasing the number of pillars on the semiconductor substrate. The increased semiconductor substrate surface area allows for a greater capacity for storing hydrogen. The thinner the pillars, the more pillars can be mounted on the same semiconductor substrate, thus achieving a better surface-to-volume ratio. Therefore, it is recognized that thin pillars allow for more pillars and thus contribute to increasing the capacity for storing hydrogen.

[0032] In principle, the pillars can have any length. However, having a length greater than 1 micron, such as greater than 3 microns, can be advantageous. Such a length can result in a good surface-to-volume ratio while being easy to fabricate.

[0033] The core of the pillar can comprise a semiconductor material, such as silicon, GaN or AlGaN.

[0034] As previously mentioned, the shell of the pillar contains Mg3N2 and / or a plurality of GaN particles. The shell surrounds the core. For example, the shell can surround the sidewalls of the pillar. The shell can encircle the circumference of the pillar.

[0035] In the following, a shell containing Mg3N2 will be discussed. Mg3N2 is also known as magnesium nitride. Magnesium nitride can be epitaxially grown on both <100> and <111> crystal orientations of the core of the column (e.g., on the <100> side or the <111> side). Magnesium nitride can be grown, for example, by sputtering on a silicon substrate (e.g., on a silicon column), by metal-organic vapor deposition, or by plasma-assisted molecular beam epitaxy (MBE). The Mg3N2 shell can be doped, for example, silicon-doped. The doped Mg3N2 shell can be used as a reversible hydrogen storage material.

[0036] The shell of the column can contain graphitic Mg3N2. Advantageously, graphitic Mg3N2 can embed hydrogen to allow hydrogen storage. In graphitic Mg3N2, Mg and N atoms form a crystal structure corresponding to graphite. Graphitic Mg3N2 can be regarded as one or more layers, where each individual layer has a hexagonal lattice, such as the hexagonal lattice of graphite, and where each hexagon of the hexagonal lattice contains both Mg atoms and N atoms.

[0037] The inventors have recognized that the formation of potential energy wells promotes the binding of hydrogen. The London dispersion forces in the embedded material can give hydrogen molecules a binding affinity higher than that of conventional adsorption by chemisorption or physical adsorption. Physical adsorption materials adsorb molecular hydrogen through van der Waals interactions, which are typically less than 10 kJ·mol -1 . The London dispersion forces from the electron cloud on the crystal surface are favorable for hydrogen adsorption. The electric potential V(r) seen by the hydrogen molecules stored in graphitic magnesium nitride can be written as V(r) = E(Mg3N2 + H2) - E(Mg3N2) - E(H2).

[0038] As described in RSC Adv., 2017, 7, 33953 (which is incorporated herein by reference), the gas density inside the potential energy well is higher than that outside the potential energy well by a factor, where V is the depth of the potential energy well, k B is the Boltzmann constant, and T is the temperature. The hydrogen storage weight efficiency of graphitic Mg3N2 can be as high as 15.2 wt%.

[0039] Alternatively, the shell of the column can contain Mg3N2 with other crystal structures in addition to graphitic Mg3N2. For example, the shell of the column can contain Mg3N2 with a cubic crystal structure, i.e., cubic Mg3N2. Cubic Mg3N2 has a lower in-plane lattice constant than silicon.

[0040] The shell of the column can contain Mg3N2 in the form of a thin film.

[0041] The thin film can be a single molecular layer. Alternatively, the thin film can include several molecular layers. The thin film can be grown, for example, by sputtering, by plasma-assisted MBE growth, or by metal-organic chemical vapor deposition. The thickness of the thin film can be less than, for example, 1 micron, for example less than 100 nm, for example less than 10 nm.

[0042] It is recognized that the shell can include a second thin film in addition to the Mg3N2 thin film. The second thin film can contain, for example, gallium nitride. The second thin film can contain Mg (x) Ga (1-x) N (y) and / or Ga 12 N 12 and / or Ga 24 N 24 and / or MgGa 11 N 12 .

[0043] It is further recognized that thin films of gallium nitride and / or Mg (x) Ga (1-x) N (y) and / or Ga 12 N 12 and / or Ga 24 N 24 and / or MgGa 11 N 12 can be used in the shell, where the shell does not contain Mg3N2 or GaN particles. Such a shell can still have advantages similar to those discussed in connection with the first aspect of the present invention.

[0044] In the following, shells containing GaN particles will be discussed. The term GaN particles can be interpreted herein as any kind of roughness or perturbation on the side surface of the column of GaN. The GaN particles can be nanocrystals. The GaN nanocrystals can be regarded as GaN crystal particles adapted within a sphere with a diameter of 500 nm, or preferably adapted within a sphere with a diameter of 100 nm.

[0045] GaN particles can be formed on the core by epitaxial growth. For example, GaN particles can be formed on the core by Stranski–Krastanov or Volmer–Weber growth. Alternatively, GaN particles can be formed by sputtering GaN. At least under some conditions, sputtering forms small particles (e.g., nanoparticles or nanocrystals), resulting in a rough surface. Alternatively, GaN particles can be deposited on the core of the column as an aerosol or colloid. The size of the GaN particles can be below 50 nm, preferably below 5 nm. The GaN particles can be stacked on top of each other. The stacked GaN particles can be separated by grain boundaries and / or by free space. The stacked GaN particles can form a porous shell. In such a porous shell, hydrogen can travel through the pores between the GaN particles deep into the shell and then be trapped in the GaN particles.

[0046] The shell can include a plurality of GaN particles forming the rough surface of the shell, wherein the rough surface of the shell of the column has a root mean square roughness greater than 1 nm. The root mean square roughness is defined as the quadratic mean or root mean square average of the profile height deviation with respect to the average line. The profile height deviation can be measured, for example, by atomic force microscopy.

[0047] A plurality of GaN particles having the above surface roughness can form a crystal or cage-like structure. The GaN particle structure can be formed similar to how quantum dots are formed. The binding affinity for particle formation is high, and the structure is arranged to bind hydrogen. The cage effect of the crystal structure of the GaN particles gives a hydrogen storage capacity similar to that of buckyballs or fullerenes. Thus, one or more hydrogen atoms can be stored in each GaN particle.

[0048] It can be particularly advantageous if the rough surface of the shell of the column has a root mean square roughness in the range of 1 nm to 10 nm, or in the range of 1 nm to 5 nm. In such a range, the hydrogen storage weight efficiency can be particularly high.

[0049] The thickness of the shell containing GaN particles can be below, for example, 500 nm, for example below 100 nm, for example below 10 nm.

[0050] The thickness of the shell can be less than 10 nm. For example, when placing a semiconductor substrate and at least one column in an electric field, a shell with a thickness less than 10 nm (which is referred to herein as a thin shell) can be advantageous. The thin shell can promote a large field intensity. The thin shell may be cost-effective because hydrogen can be stored most efficiently in the outermost part of the shell. Thus, if only the outermost part stores hydrogen, using a thick shell may be unnecessary.

[0051] The thickness of the semiconductor substrate can be 1 mm or greater. A semiconductor substrate with a thickness of 1 mm or greater can advantageously withstand pressure, for example, during the manufacturing process or when the device is in use. For example, the semiconductor substrate can be used as part of the wall in a pressurized container.

[0052] The shell of the column can be epitaxially aligned with the core of the column. When the core and the shell are epitaxially aligned, they share crystal periodicity in at least one direction at least at the interface between the core and the shell. The shell of the column can contain, for example, cubic and / or graphite-type Mg3N2 and / or GaN particles. When the core and the shell are epitaxially aligned, there may be a low defect density in the shell and / or a low defect density at the interface between the core and the shell. The defects can be, for example, dislocations. The defects can provide deep energy states, which may have an adverse effect on hydrogen storage. Therefore, a low defect density can improve hydrogen storage, for example, improving the hydrogen storage weight efficiency.

[0053] The core of at least one column can contain silicon and / or gallium nitride and / or aluminum nitride and / or aluminum gallium nitride. The crystal orientation of the material of the core of at least one column can be, for example, <100> or <111>. The core of the column can be epitaxially aligned with the semiconductor substrate. The core of the column can contain the same material as the substrate. For example, the core of the column can be made of silicon, while the substrate is also made of silicon. Such a silicon core can be etched out of the substrate. Alternatively, the core of the column can be made of another material different from the substrate. For example, the core of the column can be made of and / or gallium nitride and / or aluminum nitride and / or aluminum gallium nitride, while the substrate is made of silicon.

[0054] At least one column can contain a heterojunction, where the heterojunction is configured to form an electron gas. The heterojunction can be configured to form an electron gas through band bending. The electron gas can be formed at the interface between the core of the column and the shell of the column. As previously described, the electron gas promotes the formation of a potential energy well, such that hydrogen is bound by London dispersion forces. Therefore, hydrogen can bind to the heterojunction. The heterojunction can be formed at the interface between the core and the shell. The heterojunction can be formed at the interface between the core and the Mg3N2 shell, or between the core and one or more GaN particles of the shell.

[0055] The device can include a flow channel configured to allow a flow of hydrogen gas to pass through, where at least one column is disposed in the flow channel. The device further includes at least two electrodes configured to apply an electric field between the core of the column and the hydrogen gas in the flow channel. The electric field can control the binding and release of hydrogen. For example, the electric field can be used to reduce the depth of the potential energy well to release hydrogen, or increase the depth of the same potential energy well for binding hydrogen.

[0056] According to a second aspect, there is provided a method for manufacturing a device for hydrogen storage, the method comprising:

[0057] providing a layer of semiconductor material on a semiconductor substrate; and

[0058] Forming a core of at least one pillar by etching a semiconductor material layer; and

[0059] Providing Mg3N2 or GaN particles as a shell surrounding the core of at least one pillar, wherein the shell is provided by sputtering or metal-organic chemical vapor deposition.

[0060] The semiconductor material layer can be provided by epitaxial growth, for example, by metal-organic chemical vapor deposition or by sputtering.

[0061] The method may further include a lattice mismatch between the core of the pillar and the GaN material, and providing GaN particles as a shell surrounding the core of at least one pillar by epitaxial growth in a Stranski-Krastanov or Volmer-Weber growth mode. Thus, the GaN particles can be formed by strain-driven self-assembly. Thus, the GaN particles can be quantum dots. The self-assembled GaN particles can provide a high particle density and / or small particles and / or a suitable surface roughness. This can be advantageous for providing efficient hydrogen storage. BRIEF DESCRIPTION OF THE DRAWINGS

[0062] With reference to the accompanying drawings, the above and other objects, features, and advantages of the inventive concept will be better understood through the following illustrative and non-limiting detailed description. In the drawings, like reference numerals will be used for like elements unless otherwise noted.

[0063] Figure 1A A cross-section of the device is shown in a side view.

[0064] Figure 1B A cross-section of the device is shown in a top view.

[0065] Figure 2 A cross-section of the device is shown in a side view.

[0066] Figure 3 The device is shown in a perspective view.

[0067] Figure 4 A layer of graphite-type Mg3N2 is shown.

[0068] Figure 5 A cross-section of the device is shown in a side view.

[0069] Figure 6 A cross-section of the device is shown in a side view.

[0070] Figure 7 A cross-section of the device is shown in a side view.

[0071] Figure 8 A cross-section of the device is shown in a side view.

[0072] Figure 9 is a flow chart of a method. Detailed implementation manners

[0073] In the following, the technical content and detailed description of the present invention will be described in conjunction with the accompanying drawings according to the preferred implementation manners, and it is not used to limit the scope of the claims. The present invention can be implemented in many different forms and should not be construed as limited to the implementation manners set forth herein; on the contrary, these implementation manners are provided to be thorough and complete and to fully convey the scope of the present invention to those skilled in the art.

[0074] Figure 1A and Figure 1B shows a cross-section of the device 1. Figure 1A is a side view of the cross-section of the device 1. Figure 1B is a top view of the cross-section of the same device 1, where the cross-section is a cross-section along the Figure 1A line A-A in. The shown device 1 includes a semiconductor substrate 2 on which a plurality of pillars 10 are arranged.

[0075] Each pillar 10 includes a core 12 and a shell 14. As Figure 1B shown, the core 12 and the shell 14 can have a circular cross-section. Alternatively, the core 12 and the shell 14 can have other shapes such as a hexagonal cross-section. The shell 14 surrounds the core, for example, by extending on the side surface of the core 12 to surround the core. As shown, the shell 14 can additionally extend on the top surface of the core 12. The Mg3N2 and / or GaN particles 16 of the shell 14 can cover the side surface of the core 12. For example, the Mg3N2 and / or GaN particles 16 of the shell 14 can completely or partially cover the side surface of the core 12. The Mg3N2 and / or GaN particles 16 of the shell 14 can cover at least 30%, for example, at least 70% of the surface area of the side surface of the core 12.

[0076] The core 12 and the shell 14 can contain different materials. Therefore, an interface between the core 12 and the shell 14 can form a heterojunction 20. Such a heterojunction is shown in Figure 1A and Figure 1B in. The heterojunction 20 can be configured to form an electron gas. For example, the core 12 can be made of AlGaN, while the shell 14 is made of GaN, or vice versa. At the interface between such a core 12 and the shell 14, an electron gas can be formed. The electron gas can be regarded as a two-dimensional electron gas wrapped around the core 12. Similarly, a heterojunction 20 can be formed at the interface between the core 12 and the Mg3N2 shell, or between the core and one or more GaN particles of the shell 14.

[0077] Figure 2A cross-section of the device 1 including the flow channel 30 is shown. The flow channel 30 is configured to allow the flow 32 of hydrogen to pass through, and at least one column 10 is arranged in the flow channel 30. The device 1 further includes two electrodes 34 configured to apply an electric field between the core 12 of the column 10 and the hydrogen in the flow channel 30.

[0078] The flow channel 30 can be any form of pipe, box or container through which the hydrogen flow can pass. The flow channel 30 can include a wall 36 configured to prevent the escape of hydrogen. One electrode 34 can be arranged on the substrate 2, for example on the back surface of the substrate 2. The other electrode 34 can be arranged at a different position of the flow channel 30, for example on the wall 36 of the flow channel 30. By applying different electric potentials to the two electrodes 34, an electric field can be applied across the shell 14 of each column 10. Here, the substrate 2 and / or the core 12 can be doped so that most of the potential drop occurs across the shell 14, thereby increasing the electric field in the shell 14.

[0079] The flow channel 30 can be configured such that the substrate 2 having the column 10 can be removed. Thus, for example, in the above loading step, by applying a first electric field, the shell 14 of the column 10 can be loaded with hydrogen in the flow channel 30. Then, the substrate 2 having the column 10 can be removed and transported elsewhere. The hydrogen stored in the shell 14 of the column 10 can then be released, for example, in the above release step. For example, the substrate 2 having the column 10 can be placed in another flow channel 30, and a second electric field can be applied across the shell 14 of the column 10. The second electric field can have a direction opposite to that of the first electric field. As an alternative to removing the substrate 2 having the column 10, for both the loading step and the release step, they can remain in the same flow channel 30.

[0080] The thickness of the substrate 2 can be 1 mm or greater. This can be advantageous if there is a pressure difference between the front and back surfaces of the substrate 2. For example, if the substrate 2 forms part of the wall 36 of the flow channel 30.

[0081] Figure 3 The device 1 is shown in perspective. The shell 14 of the column 10 of the shown device 1 contains graphite-type Mg3N2. As seen in the enlarged portion of the figure, the shown column 10 has a shell 14 that includes a single layer 17 of graphite-type Mg3N2 wrapped around the core 12 of the column 10. Alternatively, the column 10 can have a shell 14 that includes multiple layers of graphite-type Mg3N2. Each individual layer 17 of graphite-type Mg3N2 has a hexagonal lattice, similar to the hexagonal lattice of graphite. The layers 17 of graphite-type Mg3N2 are shown in Figure 4 where the magnesium atoms 18 are shown as dotted textures, and the nitrogen atoms 19 are shown in white. The dashed squares are a guide to the viewing angle.

[0082] As an alternative to the shell 14 containing the graphite-type Mg3N2, the shell may contain other forms of Mg3N2, such as cubic Mg3N2.

[0083] Figures 5 to 7 It is shown that the shell 14 may contain GaN particles 16. Figures 5 to 7 A cross-section of the device 1 viewed in a side view is shown. As Figures 5 to 6 seen, the GaN particles 16 may be dispersed on the side surface of the core 12 and do not cover the entire surface area of the side surface of the core 12. The GaN particles 16 may cover, for example, at least 30% or at least 70% of the surface area of the side surface of the core 12. Alternatively, as Figure 7 seen, the GaN particles 16 may cover the entire surface area of the side surface of the core 12.

[0084] The GaN particles 16 may grow epitaxially on the side surface of the core 12. The GaN particles 16 may grow epitaxially in a Stranski-Krastanov or Volmer-Weber growth mode. Such GaN particles 16 may be lattice-mismatched with the core 12 and formed by strain-driven self-assembly. Such GaN particles 16 may have the shape of a pyramid, truncated pyramid, or dome. Figure 5 It is shown how the GaN particles 16 having a pyramid shape may look in a cross-section.

[0085] Figure 8 It is shown that multiple shells 14 may be used. Figure 8 A cross-section of the device 1 in a side view is shown. The shown device 1 includes a first shell 14' and a second shell 14". The first shell 14' may be a Mg3N2 shell. The second shell 14" may be a shell containing GaN particles 16.

[0086] Figure 9 A flowchart of a method 100 for manufacturing the device 1 according to the first aspect is shown. According to the method 100, a semiconductor material layer is provided on a semiconductor substrate 2 (S102). The semiconductor material layer may be provided by epitaxial growth. Then, at least one core 12 of the pillar 10 is formed by plasma etching the semiconductor material layer with a chlorine plasma (S104). For example, the semiconductor material layer may be patterned by lithographic means (such as by nanoimprint lithography or photolithography) and etched to form a columnar structure, which will subsequently become the core 12 of the pillar 10. After forming at least one core 12 of the pillar 10 (S104), Mg3N2 or GaN particles 16 are provided as a shell 14 around at least one core 12 of the pillar 10 (S106). This is achieved by sputtering or metal-organic chemical vapor deposition.

[0087] The core 12 of the column 10 may be lattice mismatched with the GaN material. For example, the core 12 of the column 10 may comprise additional materials other than GaN. Then, GaN particles 16 may be provided as a shell 14 (S106) surrounding the core 12 of at least one column 10 by epitaxial growth in a Stranski-Krastanov or Volmer-Weber growth mode. For example, when growing several monolayers (e.g., 8 to 10 monolayers) of a shell material that is lattice mismatched with the core 12, the monolayers may rearrange during a self-assembly process to form quantum dots. The quantum dots may be regarded as GaN particles 16 that form a rough surface.

[0088] Accordingly, the quantum dots of the shell 14 may be self-assembled quantum dots. The quantum dots may be, for example, Stranski-Krastanov quantum dots. Thus, in addition to the quantum dots, the shell 14 may also include a wetting layer. Alternatively, the quantum dots of the shell 14 may be Volmer-Weber quantum dots. The self-assembled quantum dots may provide a high quantum dot density and / or small quantum dots. This may be advantageous for achieving efficient hydrogen storage.

[0089] Under some conditions, the GaN particles 16 are provided by means other than Stranski-Krastanov or Volmer-Weber growth. For example, the GaN particles 16 may be provided as droplets sputtered onto the side of an etched column. Alternatively, the GaN particles 16 may be provided as an aerosol or colloid deposited on the side of an etched column.

[0090] In the foregoing, the inventive concept has been described mainly with reference to a limited number of examples. However, as will be readily understood by those skilled in the art, other examples are equally possible within the scope of the inventive concept as defined by the appended claims, in addition to the examples disclosed above.

Claims

1. A device (1) for hydrogen storage, comprising: A semiconductor substrate (2); At least one column (10) disposed on the semiconductor substrate (2), the at least one column (10) comprising a core (12) and a shell (14), the core (12) of the column (10) containing a semiconductor material, and the shell (14) of the column (10) surrounding the core (12) of the column (10), the shell (14) containing: Mg3N2; and / or A plurality of GaN particles (16); Wherein the device (1) further comprises a flow channel (30) configured to allow a flow (32) of hydrogen gas to pass through, wherein the at least one column is disposed in the flow channel (30), and the device (1) further comprises at least two electrodes (34) configured to apply an electric field between the core (12) of the column (10) and the hydrogen gas in the flow channel (30).

2. The device (1) according to claim 1, wherein the shell contains graphite-type Mg3N2.

3. The device (1) according to claim 1 or 2, wherein the shell (14) of the column (10) contains Mg3N2 in the form of a thin film.

4. The device (1) according to any one of the preceding claims, wherein the shell contains a plurality of GaN particles (16) forming a rough surface of the shell (14), and wherein the rough surface of the shell (14) of the column (10) has a root mean square roughness greater than 1 nm.

5. The device (1) according to any one of the preceding claims, wherein the thickness of the shell (14) is less than 10 nm.

6. The device (1) according to any one of the preceding claims, wherein the thickness of the semiconductor substrate (2) is 1 mm or greater.

7. The device (1) according to any one of the preceding claims, wherein the shell (14) of the column (10) is epitaxially aligned with the core (12) of the column (10).

8. The device (1) according to any one of the preceding claims, wherein the core (12) of the at least one column (10) contains gallium nitride and / or aluminum nitride and / or aluminum gallium nitride.

9. The device (1) according to any one of the preceding claims, wherein the at least one column (10) contains a heterojunction (20), and wherein the heterojunction (20) is configured to form an electron gas.

10. A method (100) for manufacturing the device according to any one of claims 1 to 9, the method (100) comprising: Providing a semiconductor material layer (S102) on a semiconductor substrate (2); And Forming a core (12) of at least one column (10) by etching the semiconductor material layer (S104); and Providing Mg3N2 or GaN particles as a shell (14) surrounding the core (12) of the at least one column (10), wherein the shell (14) is provided by sputtering or metalorganic chemical vapor deposition; Disposing the substrate (2) having the at least one column (10) in a flow channel (30); At least two electrodes (34) are arranged such that an electric field is applied between the core (12) of the column (10) and hydrogen by applying different electric potentials to two of the at least two electrodes (34).

11. The method (100) according to claim 10, wherein there is a lattice mismatch between the core (12) of the column (10) and the GaN material, and GaN particles are provided as the shell (14) around the core (12) of the at least one column (10) by epitaxial growth in a Stranski-Krastanov or Volmer-Weber growth mode (S106).

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